Cellular Respiration

Redox Reactions in Cellular Respiration

Redox reactions are fundamental to cellular respiration, involving the transfer of electrons between molecules. The mnemonic OIL RIG stands for Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

• Oxidation: Loss of electrons from a molecule.

• Reduction: Gain of electrons by a molecule.

• Example: In cellular respiration, glucose is oxidized and oxygen is reduced.

Overall Equation of Cellular Respiration

The process of cellular respiration can be summarized by the following equation:

• $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

• Inputs: Glucose and oxygen

• Outputs: Carbon dioxide, water, and ATP

Electron Carriers in Cellular Respiration

Electron carriers such as NAD+ and FAD play a crucial role in transporting electrons during cellular respiration.

• NAD+: Accepts electrons to become NADH

• FAD: Accepts electrons to become FADH2

• Function: Shuttle electrons to the electron transport chain

Stages of Cellular Respiration and Their Locations

Cellular respiration occurs in several stages, each with distinct locations within the cell:

• Glycolysis: Cytoplasm

• Pyruvate Oxidation: Mitochondrial matrix

• Citric Acid Cycle (Krebs Cycle): Mitochondrial matrix

• Oxidative Phosphorylation: Inner mitochondrial membrane

Major Accomplishments of Each Stage

• Glycolysis: Breaks down glucose into pyruvate, produces ATP and NADH

• Pyruvate Oxidation: Converts pyruvate to acetyl-CoA, produces NADH and CO2

• Citric Acid Cycle: Completes glucose breakdown, produces ATP, NADH, FADH2, and CO2

• Oxidative Phosphorylation: Generates most ATP via electron transport chain and chemiosmosis

Inputs and Outputs of Glycolysis

• Inputs: Glucose, 2 ATP, 2 NAD+

• Outputs: 2 Pyruvate, 4 ATP (net gain 2 ATP), 2 NADH

Substrate Level Phosphorylation

Substrate level phosphorylation is the direct transfer of a phosphate group to ADP to form ATP, occurring in glycolysis and the citric acid cycle.

Pyruvate Oxidation, Citric Acid Cycle, and Oxidative Phosphorylation

• Pyruvate Oxidation: Inputs: Pyruvate, NAD+; Outputs: Acetyl-CoA, NADH, CO2

• Citric Acid Cycle: Inputs: Acetyl-CoA, NAD+, FAD; Outputs: CO2, NADH, FADH2, ATP

• Oxidative Phosphorylation: Inputs: NADH, FADH2, O2; Outputs: ATP, H2O

Oxaloacetate and Citrate in the Citric Acid Cycle

• Oxaloacetate: Combines with acetyl-CoA to form citrate

• Citrate: First product of the citric acid cycle

Mitochondrial Structure and Chemiosmosis

The inner membrane of the mitochondria is highly folded (cristae), increasing surface area for the electron transport chain and ATP synthesis via chemiosmosis.

Electron Transport Chain and Chemiosmosis

• Electron Transport Chain: Transfers electrons, pumps protons to create a gradient

• Chemiosmosis: Uses proton gradient to drive ATP synthesis

Fermentation

• Occurs: When oxygen is unavailable

• Major Accomplishment: Regenerates NAD+ for glycolysis, allows continued ATP production

Facultative vs. Obligate Anaerobes

• Facultative Anaerobes: Can survive with or without oxygen

• Obligate Anaerobes: Cannot survive in the presence of oxygen

Alternative Food Sources for Energy Production

• Proteins and fats: Can be broken down and enter cellular respiration at various points

Regulation of Cellular Respiration

• Biofeedback: Cellular respiration is regulated by feedback mechanisms, such as ATP and ADP levels

Photosynthesis

Autotrophs and Heterotrophs

• Autotrophs: Organisms that produce their own food via photosynthesis (e.g., plants)

• Heterotrophs: Organisms that consume other organisms for energy

Leaf Cells and Photosynthesis

• Photosynthesis occurs: Mainly in the mesophyll cells of leaves

Importance of Photosynthesis

• Critical Role: Provides energy and organic molecules for all life on Earth

Overall Chemical Equation of Photosynthesis

• $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

• Inputs: Carbon dioxide, water, light energy

• Outputs: Glucose, oxygen

Photosynthesis Process: Two Sets of Reactions

• Light Reactions: Occur in thylakoid membranes, produce ATP and NADPH

• Calvin Cycle: Occurs in stroma, uses ATP and NADPH to fix carbon dioxide into glucose

Multiple Pigment Molecules

• Benefit: Allow plants to absorb a broader spectrum of light, increasing photosynthetic efficiency

Why Plants Appear Green

• Chlorophyll: Absorbs red and blue light, reflects green light

Sequence of Events in Light Reactions

• Absorption of light by chlorophyll

• Excitation of electrons

• Electron transport chain produces ATP and NADPH

• Oxygen is released as a byproduct

Inputs and Outputs of Light Reactions

• Inputs: Water, light, NADP+, ADP

• Outputs: Oxygen, ATP, NADPH

Anatomy of the Thylakoid and ATP Production

• Thylakoid: Membrane-bound compartment in chloroplasts

• Function: Houses electron transport chain and ATP synthase for ATP production

Calvin Cycle: Four Major Steps

• Carbon fixation

• Reduction

• Release of G3P (glyceraldehyde-3-phosphate)

• Regeneration of RuBP (ribulose bisphosphate)

Relationship Between Calvin Cycle Product, Glucose, and Cellular Respiration

• G3P: Can be converted to glucose, which is used in cellular respiration

Relationship Between Light Reactions and Calvin Cycle

• ATP and NADPH: Produced in light reactions, used in Calvin cycle

Photosynthesis vs. Cellular Respiration

• Not Opposites: Both are essential, interconnected processes in the energy cycle of life